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- Hi and welcome back.

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Here we've got the Classes
and Objects Coding Exercise

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and this is getting more and more

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complicated as time goes by,

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but hopefully we'll be able to do it.

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Now, if you have not looked into the

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exercise prior to this video,

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I would recommend you
go and check that out

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and try do it and then we'll come back

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and explain what happened.

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This coding exercise has three steps.

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First, it requires us to complete

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an implementation of
three methods of a class.

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The first one is the "_init_" method.

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We should take one argument name

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and it should initialise
self.name to be the argument

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and self.items to be an empty list.

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Let's start with that.

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Let's not hold too much information

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in our heads to begin with.

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So, we're going to need
name as the argument.

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We've got the _inti_
method which always has

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self and then the name
as the other argument.

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Then we're going to initialise self.name

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to be the argument,

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and self.items To be an empty list.

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Self.name is going to be the argument name

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and self.items is going
to be an empty list.

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Whenever we create a store object,

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it's going to have these
two properties in it.

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Let's move on to the second instruction.

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The add-item method, which
should append a dictionary

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representing an items to
the store's items property.

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The dictionary should
have keys, name and price.

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Okay, so the comment down
here's a bit more succinct,

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it tells us exactly what to do.

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Create a dictionary with
the keys, name and price

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and append that to the self.items.

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Notice how the add-item
method has two arguments

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other than self, name and price.

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So, we're going to create a dictionary

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with keys, name and price and I think

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it's reasonable to assume
that this dictionary

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is also going to use these two arguments.

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So we're going to do
an item is a dictionary

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with keys, name and that's
going to be something price,

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and that's going to be something else.

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And this is our dictionary

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and has two keys, name and price

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and the values are going
to be the argument values.

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Now, this is not explicit in the exercise

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because I want you to
start making assumptions

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about the code you're seeing

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and I think this is a
reasonable assumption to make.

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So, we've got name, and that's
going to use the argument

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and price and that's
going to use the argument.

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What this means is that when
you call this add-item method,

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you're going to pass in the name

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and the price of the item you want to add,

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and that's going to create the item

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and add it to the store for you.

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All you have to do, is not create an item

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and give it to this method,

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but just give it the values

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that you want to add
to the store as items.

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Naturally, we have to
make sure to add the item.

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So, self.items.append(item)

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That will append the item into self.items.

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And that's it.

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The stock_price method,

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which is a third instruction here,

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which should add up each item price inside

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self.items to come up with
a total and return that.

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Okay, so let's add up all
of the prices in self.items.

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In a previous exercise, we looked at

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how to do this in one way,

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which was to create a total = 0 variable

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and then iterate over
for item in self.items

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iterate over all the items,

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and say total += item(price)
and then return total.

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This would totally work.

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We start with zero, we go over each item,

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we add to the total the price of the item,

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then we return the total.

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However, now that we've
looked at list comprehension,

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there's a better way of doing it,

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which is return sum(item.price)

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for item in self.items.

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This is substantially more concise

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and as soon as you get
more to grips with Python,

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if you haven't already,

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I think this is actually more readable,

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because you can very quickly see that

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you're getting all the item prices,

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and you're adding them all up.

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Once again, to recap
what's happening here is

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we're iterating over the items,

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but we're only putting the item price

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into our new list, which we're creating

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with list comprehension.

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When we have a list of item prices,

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we're summing them all up
and we're returning that.

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So, let's check the solution.

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And there we have it,
the solution is correct.

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So, we've learned a bit more
about how these objects work,

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and I'll see you in the very next video.